1. Field of the Invention
The present invention relates to a semiconductor device using an oxide semiconductor and a manufacturing method thereof.
In this specification, the term semiconductor device refers to all devices that can function by utilizing semiconductor characteristics, and electrooptic devices, semiconductor circuits, and electronic devices are all semiconductor devices.
2. Description of the Related Art
In recent years, transistors used for many liquid crystal display devices and light-emitting display devices typified by flat panel displays have been formed with silicon semiconductors, such as amorphous silicon or polycrystalline silicon, over a glass substrate.
Attention has been being directed to a technique in which, instead of such silicon semiconductors, oxide semiconductors are used for transistors.
Examples of the oxide semiconductors are zinc oxide, which is a metal oxide of one metal element, and In—Ga—Zn—O-based oxide, which is a homologous compound. Techniques are disclosed in which such oxide semiconductors are used to form transistors for switching elements or the like in pixels of display devices (see Patent Documents 1 to 3).